Proposed Missions Could Deflect Space Rocks Like Asteroid Apophis

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While scientists keep a close watch on the myriad space rocks
near Earth, they don’t yet have a solid plan on what to do if one
appears headed on a collision course toward our planet.

Two new studies propose potential spacecraft missions that would
collide with asteroids in an attempt to deflect them away from
our planet. Such missions, some researchers say, may be among our
best hopes to ward off
asteroids that may pose a threat to Earth.

One concept from researchers in China involves deflecting an
asteroid with a spacecraft propelled by solar sails, giant
mirrors that fly through space via the force of sunlight
reflecting off them. A possible target is the
asteroid known as Apophis, named after the Egyptian god of
darkness because of fears that it might crash into Earth.

The researchers noted that giving Apophis a tiny shove at a key
moment in 2029 would help ensure that it would not approach Earth
in 2036, the year that it is forecasted to come near. The
scientists calculated that a solar sail could hurl a spacecraft
fast enough at Apophis to potentially knock it off course.
[ Photos:
Asteroids in Deep Space ]

"The impact velocity can be as high as 100 kilometers per second
(223,700 mph), which is much higher than the impact velocity of a
regular spacecraft, which is about 30 kilometers per second
(67,100 mph)," study lead author Shengping Gong at Tsinghua
University in Beijing told SPACE.com.

The mission would involve two probes. One would smash into its
target asteroid at more than 30,000 mph (48,000 kph), while the
other would orbit the asteroid six months beforehand to observe
its behavior before and after impact.

However, Don Quijote or any other mission aiming to slam into an
asteroidsto deflect it would need to analyze such collisions in
greater detail than before thought, according to scientists at
the Open University in England and their colleagues. [ Video: Asteroid
Collision Watch ]

Instead of measuring only an asteroid's orbit before and after
impact, researchers found that its diameter, reflectivity and
surface roughness would also have a large effect on how it would
react to a collision. As such, these details need to monitored
closely as well, significantly altering such missions.

In addition to radio transmitters to help pin down an asteroid's
orbit, these spacecraft would need to carry sophisticated imaging
arrays, and possibly seismic sensors on the space rock to see if
it would break apart upon impact.

"In order for the mission to succeed, you have to characterize
the physical properties to distinguish effects from the
deflection and effects from other non-gravitational
perturbations," study lead author Stephen Wolters, an astronomer
now at NASA's Jet Propulsion Laboratory in Pasadena, Calif., told
SPACE.com.

Picking an asteroid target

The researchers do note that the asteroids they used in their
calculations are not immediate threats.

The
asteroid Apophis is expected to fly harmlessly by Earth on
April 13, 2036, with only a 1-in-233,000 chance of hitting our
planet, while neither of the two asteroids studied for the Don
Quijote mission, designated 2002AT4 and 1989ML, is close to
crossing Earth's orbit.

Although Apophis was picked for the study only as an example,
"the results are universal" and could apply to other asteroids,
Gong said.

"The idea for the mission was not to deflect a dangerous
asteroid, but to deflect a safe one a little bit," Wolters said
of his team's results. "This is practice so that we are prepared
when there is a real danger. At the moment you might need a
decade or more to prepare a real deflection mission. By having
test missions, you cut down on that time, so you are prepared if
you find an asteroid with fewer years until impact."

Follow SPACE.com contributor Charles Q. Choi on Twitter
@cqchoi. Visit SPACE.com
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